Japanese Patent Application Publication No. 2005-46753 (JP2005-46753A) shows a conventional reactor that uses high-temperature air combustion technology. A fuel gas combustion apparatus used in a reactor employing high-temperature air combustion technology includes a burner assembly that injects fuel gas into a combustion chamber and a combustion air supply apparatus of alternating heat exchange type (hereinafter sometimes referred to simply as a combustion air supply apparatus). Japanese Patent Application Publication No. 10-205743 (JP10-205743A) shows a combustion apparatus that burns low-caloric fuel gas such as blast furnace gas and fart by heating the gas with a regenerator that has air permeability and is provided in the combustion air supply apparatus for heat exchange. The combustion apparatus shown therein burns the low-caloric fuel gas by using as an ignition burner a pilot burner using high-caloric fuel gas as fuel gas. The pilot burner shown therein injects combustion air together with fuel gas into a reactor wherein the combustion air is supplied from a combustion air supply pipe disposed concentrically with a fuel gas supply pipe for supplying the fuel gas.
The pilot burner is intended for use as an ignition burner, but is also used to maintain stable combustion while the temperature inside the reactor is as low as 500 to 600° C. (degrees C.), for example, immediately after the ignition. After the temperature inside the reactor has reached a high temperature, the pilot burner may be turned off. However, the low-caloric fuel gas is not enough to produce a high-temperature air combustion state. Therefore, in a fuel gas combustion apparatus that continuously supplies a fuel and burns fuel gas with the help of combustion air heated by a regenerating means, high-caloric fuel gas injected from a burner assembly using high-caloric fuel gas as the fuel gas is mixed with combustion air heated to a high temperature with a combustion air supply apparatus of alternating heat exchange type in a space of high-temperature combustion.
In the fuel gas combustion apparatus, the high-caloric fuel gas injected from the burner assembly using the high-caloric fuel gas as fuel gas is mixed with the combustion air heated to a high temperature with the combustion air supply apparatus of heat exchange type. Low-caloric fuel gas may be used as fuel gas. However, when the low-caloric fuel gas is used as fuel gas, a large amount of the low-caloric fuel gas is needed and it is difficult to heat such a large amount of the low-caloric fuel gas to a high temperature. Thus, it is hard to use the low-caloric gas in conventional fuel gas combustion apparatuses.
If combustion air, which has been heated with a combustion air supply apparatus of alternating heat exchange type, is supplied to the fuel gas combustion apparatus, unburned fuel gas may be discharged together with combustion exhaust gas to be discharged. Japanese Patent Application Publication No. 9-273741 (JP09-273741A) has proposed that an injection opening of fuel gas should be disposed more inwardly than a discharge opening for combustion exhaust gas in the reactor.